Yale Astronomy Virtual Colloquium - Heidi Jo Newberg

Event time: 
Thursday, February 4, 2021 - 2:30pm
Heidi Jo Newberg
Speaker Institution: 
Rensselaer Polytechnic Institute
Talk Title: 
The Virgo Radial Merger and the Discovery of Shell Structure in the Milky Way Halo
Event description: 

Large sky surveys, and most recently the Gaia data releases, have revolutionized our knowledge of the Milky Way halo (and the disk, which will be largely ignored in this talk). As dwarf galaxies fall into the Milky Way, stars (and presumably dark matter) are stripped into long streams of stars that are incorporated into the halo. Dozens of these tidal streams have been discovered over the past two decades. However, the origin of other large halo substructures such as the Virgo Overdensity and the Hercules-Aquila Cloud remained unexplained. With the availability of Gaia data, 6D orbital information made it possible to connect the stars in these overdensities with a single dwarf galaxy radial merger. The Virgo and Hercules-Aquila overdensities contain shells, which form at the points that stars are turning around on their orbits. From these shell timing arguments, the merger event is estimated to have occurred 2.7 billion years ago. The connection between this Virgo Radial Merger and the previously identified Gaia Sausage and Gaia Enceladus Merger will be discussed.